1. Field of the Invention
The present invention relates to magnetic head supporting mechanisms for use in magnetic recording systems and, more particularly, to magnetic head supporting mechanisms for use with double-sided media.
2. Description of the Prior Art and Related Information
Magnetic head supporting mechanisms for magnetic recording systems using both sides of a flexible disk may be divided into three types in accordance with the prior art.
One type, the so-called "IBM" type, has been used since IBM Corporation first developed the flexible disk drive. In this type, magnetic heads are carried on the leading ends of spring arms and pressed through projections suspended by press springs so that they can rotate in the radial and tangential directions of a flexible disk.
As the density of the magnetic recording apparatus using the flexible disk increases, however, the above-specified structure has been found unable to position the magnetic heads in prescribed positions with sufficient accuracy. This structure has not been adopted for use in magnetic recording systems using a flexible disk of 5.25 inches or less.
Prior art supporting mechanisms adopted at present for magnetic recording systems using flexible disks of 5.25 inches or less may be divided into the following two types.
FIGS. 3(a) and 3(b) are sections showing portions of the first type prior art supporting mechanism, and FIG. 4 is a perspective view of this first type supporting mechanism. In this first type supporting mechanism (which will be called the "double sided gimbal type"), a first magnetic head 55 and a second magnetic head 59 are mounted in a gimballed manner by a first supporting plate 56 and a second supporting plate 60, respectively, to hold a flexible disk 51 therebetween through first and second pivots 54a and 58a which are formed partially in first and second rigid carriages 54 and 58, respectively. The second carriage 58 is pressed toward the first carriage 54 by a holding plate 58b and a head pressing spring 58c.
In this first type magnetic head supporting mechanism, each magnetic head is mounted in a gimballed manner and has freedom of movement in two directions (as indicated by arrows 64 and 65 in FIG. 4). The freedom of movement is determined by the torsional rigidities of the first and second supporting plates 56 and 60. The torsional rigidities are made generally low at 200 g mm/rad or less so as to improve the followability of the magnetic heads to the flexible disk 51.
In the magnetic head supporting mechanism of the second type, the first magnetic head is fixed on the first carriage whereas the second magnetic head is mounted in a gimballed manner by a holding plate on a pivot formed in a portion of a second carriage, such that the flexible disk is held between the first and second magnetic heads. The second head has freedom of movement in two directions, in a manner as has been described with reference to FIG. 4, the freedom of movement being determined by the respective torsional rigidities of the supporting plate. Such a second type magnetic head supporting mechanism is shown in U.S. Pat. No. 4,151,573 to Sirjang L. Tandon et al.
With a view to compensating the unfollowability of the flexible disk because the first magnetic head is fixed on the first carriage, it is necessary to improve the followability of the second magnetic head to the flexible disk. For this reason, the torsional rigidity of the supporting plate of the second magnetic head is generally at 150 g mm/rad or less.
In the prior art first type magnetic head supporting mechanism, as has been described hereinbefore, the first magnetic head 55 and the second magnetic head 59 are borne by the first pivot 54a and the second pivot 58a, respectively, as shown in FIG. 3(a). In case the flexible disk 51 inclines, the first and second magnetic heads 55 and 59 will incline to follow the flexible disk 51 thereby to establish a displacement from the prescribed recording and reproducing position, i.e., the so-called "off-track" condition.
This "off-track" problem will be described in detail in relation to the illustrative diagram of FIG. 5. In FIG. 5, the first supporting plate 56 carried on the first carriage 54 and the second supporting plate 60 formed on the second carriage 58 are contacted with the first and second pivots 54a and 58a respectively such that they are regulated from warping toward the respectively corresponding carriages 54 and 58 and such that they can roll on the points contacting the first and second pivots 54a and 58a. If, for example, the flexible disk 51 moves up and down or warps, the first and second magnetic heads 55 and 59 are inclined for stabilization, while holding the flexible disk 51 therebetween, until the flexible disk 51 comes into balance with the torsion of the first and second supporting plates 56 and 60, as shown in FIG. 5.
In order to retain the data compatibility of the magnetic recording system, the recording and reproducing position of a recording and reproducing medium is standardized and specified. As shown in FIG. 5, the positioning of the recording and reproducing portions of the first magnetic head 55 and the second magnetic head 59 cause displacements or off-tracks of .DELTA.X3 and .DELTA.X4, respectively, from the original recording and reproducing positions of the disk 51. As a result, if .the data are reproduced in this state, the reproductions are either incorrect, if possible, with a smaller amplitude of the reproduced signals, or impossible.
If, on the other hand, the data are recorded in that state and are reproduced by another normal magnetic recording apparatus, the amplitude of the reproduced signals decreases to make correct reproduction impossible. This can significantly drop the reliability of the magnetic recording apparatus, or cause the fatal defect that the magnetic recording apparatus will lose its compatibility.
In the second type prior art magnetic head supporting mechanism, on the other hand, the off-track condition as specified above will not occur. However, the followability of the inclination of the flexible disk is bad, since the first magnetic head is fixed. In order to attain a sufficient followability, the force (i.e., the so-called "head pressing force") for pressing the second magnetic head toward the first magnetic head must be increased. This invites a defect, however, in that the lifetime of the flexible disk is shortened.
In either the first type prior art magnetic head supporting mechanism (i.e., the double sided gimbal type) or the second type prior art magnetic head supporting mechanism (i.e., the single sided gimbal type), the first magnetic head 55 and the second magnetic head 59 (as shown in FIG. 3(a)) impact against each other through the flexible disk 51, when the second magnetic head 59 comes from the unloaded state (not-shown), in which it does not press the flexible disk 51, to the head loaded state (shown in FIG. 38(a)), in which the second magnetic head 59 presses the flexible disk 51. This impact will damage the magnetic film of the flexible disk 51 and will cause separation of the magnetic layer, depending upon how serious the damage is, to raise a problem that errors are made in the recording and reproducing operations.
In order to weaken the above-specified impact, there has been adopted in the prior art a method of damping the impact by attaching an oil damper to the second carriage to apply a braking force to the second carriage when in the head loaded state. This oil damper is expensive and raises another problem that it has such serious temperature dependencies that the oil viscosity will drop at a high temperature to degrade the damping effect and will rise at a low temperature to make the damper excessively effective.
Both the first type prior art magnetic head supporting mechanism and the second type prior art magnetic head supporting mechanism require the first and second pivots 54a and 58a, shown in FIG. 3(a). These pivots in turn raise the following problems, explained in relation to FIGS. 6 and 7, which are diagrams illustrating the coactions of the pivots and the supporting plates. For simplicity of explanation, only one head is shown, but similar explanations will apply to the other head.
In FIG. 6, the first magnetic head 55 holds the flexible disk 51 and is supported by the first supporting plate 56 having flexibility, which in turn is regulated by the first pivot 54a formed in the first carriage 54.
FIG. 7 shows the state in which the first magnetic head 55 inclines following the flexible disk 51. In this case, the first magnetic head 55 will incline following the flexible disk 51 whereas the first supporting plate 56 will have its tie bar 56y (also indicated at 56y in FIG. 4) warping to rotate on the sectional center 56b shown in FIG. 6. Since, however, the first supporting plate 56 is regulated by the first pivot 54a, it will turn as a matter of fact on the contact point between the first pivot 54a and the first supporting plate 56 (as seen from FIG. 7). By these actions, the tie bar position will be displaced, but this displacement has to be absorbed by the warp of an arm 56a (shown in FIG. 4). An excessive force is required for causing that warp.
More specifically, prior art structures having the first pivot 54a, forces are required for not only twisting the tie bar 56y but also warping the arm 56a in case the first magnetic head 55 inclines following the flexible disk 51. This requirement deteriorates the followability of the first magnetic head 55 to the flexible disk 51.
For the second supporting plate 60 and the second pivot 58a, the followability of the second magnetic head 59 to the flexible disk 51 is also deteriorated for the same reasons.
In order to compensate the deterioration of the followability, on the other hand, the torsional rigidities of the first and second magnetic head supporting plates 56 and 60 have to be reduced. As a result, the supporting plates are so thinned that they become weak relative to the external forces, thus raising another problem that the supporting plates are liable to be broken and deformed.